This disclosure relates to devices and methods for driving an image display device.
In a driving device for an image display device such as a thin film transistor (“TFT”) liquid crystal panel, it is known to cancel an offset voltage of an operational amplifier using a capacitor when an image signal is output to interconnection lines (e.g., data lines of the TFT liquid crystal panel). See, e.g., Japanese Patent Application Laid-Open No. 2002-041001, which is incorporated by reference.
FIGS. 6A and 6B illustrate a conventional configuration of a driving device designed to cancel an offset voltage of an operational amplifier by means of a capacitor. As illustrated in FIGS. 6A and 6B, the driving device 100 is includes an operational amplifier 102, a capacitor 104, an input terminal 106, and switches 108, 110, 112.
The operational amplifier 102 is configured to operate as a voltage follower. The capacitor 104 is capable of accumulating charges corresponding to an offset voltage generated in the operational amplifier 102 between two electrodes thereof, and one of the electrodes is connected to a non-inversion input terminal of the operational amplifier 102. The input terminal 106 receives an image signal to be displayed on an image display device (for example, a TFT liquid crystal panel).
The switch 108 is a SPST (single-pole/single-throw) switch and is configured to switch a connection between a data line 114 (used for displaying an image represented by the image signal) and an output terminal of the operational amplifier 102 between a connected state and a non-connected state. In FIGS. 6A and 6B, a pixel (cell) to which a voltage based on the image signal is applied by the operational amplifier 102 via the data line 114 is illustrated as the capacitor 116.
The switch 110 is a SPST switch and is configured to switch a connection between the other electrode of the capacitor 104 and an inversion input terminal of the operational amplifier 102 between a connected state and a non-connected state.
The switch 112 is a SPDT (single-pole/double-throw) switch and is configured to switch a connection between the input terminal 106 and the non-inversion input terminal of the operational amplifier 102 between a connected state and a non-connected state, while switching a connection between the other electrode of the capacitor 104 and the input terminal 106 between a connected state and a non-connected state.
The driving device 100 is provided with a signal output device (not shown) capable of outputting a switch control signal for controlling the switches 108, 110, and 112 to the switches 108, 110, and 112. When the switch control signal output from the signal output device is in an active state (for example, a high level), as illustrated in FIG. 6A, the output terminal of the operational amplifier 102 and the data line 114 are disconnected by the switch 108, the other electrode of the capacitor 104 and the inversion input terminal of the operational amplifier 102 are connected by the switch 110, and the input terminal 106 and the non-inversion input terminal of the operational amplifier 32 are connected by the switch 112, while the other electrode of the capacitor 104 and the input terminal 106 are disconnected by the switch 112.
On the other hand, when the switch control signal output from the signal output device is in a non-active state (for example, a low level), as illustrated in FIG. 6B, the output terminal of the operational amplifier 102 and the data line 114 are connected by the switch 108, the other electrode of the capacitor 104 and the inversion input terminal of the operational amplifier 102 are disconnected by the switch 110, and the input terminal 106 and the non-inversion input terminal of the operational amplifier 102 are disconncted by the switch 112, while the other electrode of the capacitor 104 and the input terminal 106 are connected by the switch 112.
As illustrated in FIG. 7, in the driving device 100 having such a configuration, before the image signal is input to the input terminal 106, the switch control signal is in a non-active state, and the switches 108, 110, and 112 are in their states as illustrated in FIGS. 6B. When the image signal is input to the input terminal 106 in such states, the switch control signal is put into an active state, and the switches 108, 110, and 112 are in their states as illustrated in FIG. 6A. As a result, an offset voltage of the operational amplifier 102 is applied to the capacitor 104, and, thus, charges corresponding to the offset voltage are accumulated in the capacitor 104.
As shown in FIG. 7, when the accumulation of the charges corresponding to the offset voltage in the capacitor 104 is completed, the switch control signal is put into a non-active state, and the switches 108, 110, and 112 are in their states as illustrated in FIG. 6B. As a result, the offset voltage of the operational amplifier 102 is canceled, and, at the same time, a voltage based on the image signal is applied to the capacitor 116 via the operational amplifier 102 and the data line 114 during a period from the start (in FIG. 7, denoted by “addressing start”) of accumulation of the charges to the capacitor 116 corresponding to the voltage corresponding to the image signal input to the input terminal 106 to the completion (in FIG. 7, denoted by “addressing end”) of accumulation of the charges corresponding to the voltage to the capacitor 116.